Impression metal



June 2, '1925. 1,539,993

E. -J. CONLEY ETAL IIPRESSION METAL Filed Aug. 22, 1923 Patented June 2, 1925.

UNITED STATES PATENT OFFICE.

EDWIN J. CONLEY, OF NEW YORK, AND GEORGE W. MULLEN, F HUSHING, NEW YORK, ASSIGNORS, BY MESNE ASSIGNMENTS, TO LEHMAIER SCHWARTZ 6'0 (10., INC., 01 NEW YORK, N. Y., A. CORPORATION 01 NEW YORK.

IMPBESSION METAL.

Application filed August 22, 1928. Serial No. 658,748.

To all whom it may concern:

Be it known that we, EDWIN J. Conner and GEORGE W. MULLEN, citizens of. the United States, and residents of 46 East 51st 5 Street, New York city, N. Y., and of Flushing, in the county of Queens and State of New York, respectively, "have invented certain new and useful Improvements in Impression Metal, of which the following is a specification.

Our present invention relates to an improvement in the art of preparing metallic surfaces, and is especially applicable to the lead used in transfer or impression plates in the electrotyping process, and to the product of the treatment. It is not limited in its application to the art herein described.

In the electrotyping art, it is common to press a thin sheet of commercial lead, approximately .03 to .04 inch thick, upon an engraved or etched surface of a harder metal, such as steel, thus transferring any design upon the steel to the lead negative.

Afterwards the lead impression is placed in a plating bath, usually of copper solution, suitable precautions well known in the trade beingused to prevent deposit of metal where it is not desired. After a proper copper deposit, thick enough to stand handling, is formed upon the design in the lead, it is stripped away and backed for use in printing.

Articles fabricated from metallic lead are readily acted upon by exposure to air, causing thelead to assume a dull appearance. It is the object of our present invention to prevent the loss of brightness possessed by the newly fabricated lead, and so to prepare the article that it resists atmospheric 1corrosion to a greater degree than untreated ead.

Lead is easily attacked by the air, especially moist air, which leads to pitting of the surface; this acts to preventclose and intimate contact between the lead and the etched plate, rendering the transfer of the design imperfect. It has heretofore been necessary to clean the lead plate immediately before use, for this reason; and'it has been found quite out of the question to prepare the plates any length of time in advance, so quantity production has been impossible.

Olean surfaces of pure metals, such as tin or lead, actin as cathodes in electroplatlng, receive rmly adhering deposits unless such metals are protected by oxidizing the surfaces immersed in the solution, or resorting to some protective film such as 011 or grease.

Another method of preparing the plate has been by pressing a sheet of tin foil into intimate contact with the impression surface of the lead by passing them through rollers. This is effective and highly useful; but in electrolytes of certain formulas it has been found to give rise to pitting from local action, tin being more electropositive than lead. Of course this spoils the copper reproduction.

ur present invention aims to provide a substantially continuous process by which metal is furnished in uniform quality ready for immedite use without further treatment of any kind, using only the elementary precautions common in the trade for maintaining the prepared surface clean,.such as avoiding contact with the fingers or other objects.

In brief the process consists in taking a strip of metal, preferably continuous, passing it through scratch-brushes which preferably revolve in a direction opposite to the lead (though if the speed be ad usted properly the motion may be in the same direction) then passing the sheet or strip through a bath of a solution of the bi-chromate of an alkali metal, then removing surplus moisture from the sheet, then washing with water and drying thoroughly, and rolling it into a compact reel, the size of which is limited only by convenience in handling. In general both surfaces of the strip or sheet may be treated as conveniently as one, and without substantial difference in expense; but the rocess may be applied to one side only. ometimes a strip of paper may be inserted between the turns of the roll of treated lead, and we have shown such a means of protection; it is preferably not a sulphite paper. We do not consider this necessary in general, and the process is the same whether or not it is done. The process forms a protective coating of lead bichromate, which preserves the surface, and prevents attack by the air.

The product is'clean metal, brush-marked upon one or both sides and having a bright surface ready for immediate use. The turns of the roll may be pressed into intimate contact, not sufiicient pressure being employed to cause the lead surfaces to adhere.

The accompanying drawing shows in Fig-- ure 1 a diagrammatic view of an arrangement for carrying out our improved process; and in Figure 2 a sam 1e of the product. The product, thoug immedlately recognizable after it has once been seen, is practically impossible to illustrate in a patent drawing; what we have shown is rather an indication than an illustration. In the drawings, A is a strip of metal, usually lead, which is to be treated by my process, A the roll from which it is taken, and A the roll in which it is finally assembled. B and B are cleaning rolls, illustrated as revolving scratch-brushes turning in the opposite direction at their points of contacts with the lead to the draft of the latter. 0-0 are guide rollers, and D indicates rollers which presses the strip of lead into the solution contained in a tank G, through which it is passed. E-E are squeegee rollers, usually,

of soft rubber composition, which are preed into close contact with the lead so as to remove as much as possible of the moisture therefrom as it is passed through the bath G; the surplus moisture runs into another tank G, whenee it may be conveyed by any suitable means to the tank G. C is a pressure roller, which of course is ordinarily mounted in sliding bearings, not shown, and which by its weight tends to bring the turns of the lead on the roll A into contact so that the clean surface is adequately protected. F is a roll of paper, from which a strip may be passed between the turns of the lead in the roll A, if found desirable; as indicated in our statement of invention this is not ordinarily necessary, but may be used if referred. G is a tank of clear water, and 1111' another pair of squeegee rolls, for removing the surplus and causing it to run into a. drain G. Any source of supply of water may be used. This is an important step in-the process, as there is thus no deposit of the salt on the surface of the metal, which may cause local action and prevent good contact. I is a blower, from which air heated in any desired manner may be passed through the pipe and nozzle I to the treated surface; obviously it may if desired be passedto both surfaces from the same source. We have not deemed it necessary to illustrate this.

In Figure 2 we have shown a fragment of the strip A, a showing an untreated portion and a showing a portion which has been brushed and treated. The lines formed on the surface are exceedingly minute and close together and while they give the surface a characteristic finish easily recognized, it is impossible to reproduce them accurately in a raving.

The so ution contained in the tank G is the bichromate of an alkali metal, usually about a 1% solution. Generally. we employ sodium bichromate, but potassium bic romate is a chemical eifiivalent; and other suitable rea ents may employed. In general the su stances named are cheap and eflicient.

The resultant metal is soft, bright, and resists the action of the electrolyte or co r plating solution very well. It is rea 1ly stripped from the deposited film of copper, and the surface wets readily, 'which renders the resistance of the bath lower and ionsumes less current, besides giving less eat.

While we have described the process as particularly applied to producing impression lead, it may be used for other purposes and other metals, as will be obvious. The process outlined forms on the metal a protective film composed of a compound of the metal with a salt of an alkali metal ;v where sodium bichromate is used, for example, a chromic salt of the metal is formed, in the case of lead (for which the process is extensively used), a lead chromate film. This is substantially non-oxidizable in air, even in damp air, not being at all hygroscopic, and protects the metal thoroughly. The washing of the protected surface might be postponed until the plate is about to be used without departing from the invention, but it is best to complete the operation as indicated herein.

We claim:

1. As a new article of manufacture, lead impression plates for electrotyping, having a surface thereof provided with a protective coating of lead bichromate.

2. As a new article of manufacture, lead impression plates for electroplating having the. surface thereof provided with minute closely spaced scratches and with a protective coating of lead bichromate.

3. Impression metal having at least one clean surface protected by a coating of a chrome salt, as described.

4. Impression lead having at least one surface protected by a metallic chrome salt.

5. Impression lead having at least one surface unoxidized and protected by a film of a lead chrome salt.

Si ed at New York city in the count of N a y w York and State of New York this 6th day of August, A. D. 1923.

EDWIN J. CONLEY. 

